The present invention relates generally to conduit installations containing electrical conductors, and more particularly to low-point drains for removing water or condensation from such electrical conduit systems that are situated in non-hazardous locations.
In commercial and industrial construction, it is common practice to contain electrical wiring in metal, or sometimes plastic, conduits. Even in relatively dry locations, moisture typically forms on the interior walls of the conduit due to condensation of water vapor in the air. In installations where metal conduits are employed, corrosion and premature deterioration of the conduit material may result. Further, an accumulation of water in the conduit system may result in creating an electrical short circuit.
Since it is for these reasons undesirable to have water accumulating inside the conduits, in situations where there are no surrounding flammable vapors or particles that could be ignited by a spark within the electrical conduit system, the problem may be eliminated by simply providing an open fitting or even a hole at various low points in the conduit system. One difficulty with merely introducing a drain hole in the metal conduit or a metal enclosure is that the hole tends to rust out and accelerate rusting of the adjacent portions of the conduit. Further, any opening in the conduit system is undesirable as it may encourage or permit insects or rodents to enter the conduit system and destroy or damage the electrical insulation.
Another conventional way of draining electrical conduit systems is to install an explosion-proof drain fitting. Use of a fitting of this type is mandatory where the installation site is designated as hazardous due to the presence of explosive vapors or dust. Standardized classifications for the various types of hazardous locations have been adopted and assigned by regulatory agencies according to the nature and type of hazard that is generally present or that may occasionally be present. For instance, at locations where oil or gas wells are being drilled or where petroleum products are being recovered, refined or processed, flammable gases may be present, including mixtures of oxygen, methane, ethane, propane, hydrogen sulfide and others. Highly flammable atmospheres may also be present in industrial areas where large quantities of flammable dust are present, such as in grain handling facilities or pulp and paper mills.
Because electrical wires and components, by their nature, may generate heat and sparks sufficient to ignite a flammable gas or other flammable mixture under even normal operating conditions, special precautions must be taken in hazardous locations in order to keep the wiring and other components isolated from the environment. At the same time, however, it is desirable to allow the conduits in such hazardous locations to drain. Presently, there are various conduit fittings and accessories commercially available that serve as low point drains for conduit systems located in hazardous locations. One such explosion-proof drain fitting is described in U.S. Pat. No. 4,467,136, issued to Wium, and has an interior filled with a sealing compound and an auxiliary member that can be oriented relative to the position of the conduit for better filling and draining. U.S. Pat. No. 2,405,927, issued to Tornblom, discloses a flame tight drain consisting of a tortious helical screw thread outlet passage that is intended to permit water to seep out, but to deter outward passage of a flame. U.S. Pat. No. 2,835,722, issued to Appleton, discloses another screw thread-type drain for an explosion-proof enclosure employing a hardened sealing compound.
Conventional explosion-proof fittings employed as low point drains often contain shot or baffles as the insulating material. Unfortunately, the soap or lubricant that is used to reduce friction when pulling wires through the conduit run tends to collect in these fittings and frequently causes the drain to clog and prevents it from operating for its intended purpose.
Furthermore, in non-classified locations there is no need to install elaborate and expensive explosion proof fittings. Nevertheless, because it is undesirable to leave an open drain hole in the system, it is common practice to employ one of the commercially available explosion-proof drain fittings despite its relatively high cost and despite the tendency of certain of these fittings to become clogged. This is due primarily to lack of availability of a suitable nonhazardous duty drain assembly. Use of an explosion-proof drain in this situation, however, adds unnecessary labor, materials and expense to the installation of the electrical system. Some types of explosion-proof drains also require the additional installation of special sealants or breather assemblies to allow adequate ventilation within the system. The industry would welcome a low cost, simple-to-install fitting that performs as a low point drain and breather device in non-hazardous locations, especially one that is free from internal baffles, special threads and sealants, and one that is easily maintained.